The present invention generally relates to wireless communications, and particularly relates to antenna impedance matching in a wireless communication device.
Impedance matching generally refers to the relationship between a source impedance and a load impedance. Maximum power transfer occurs when the source impedance matches the load impedance. For time-varying signals, matched source and load impedances also results in a minimum Voltage Standing Wave Ratio (VSWR), i.e., results in minimum signal reflections from the load.
The desirability of impedance matching is so well know that it is taken as a given that one should “match” source and load impedances as part of the design effort. While impedance matching generally offers no special challenges in environments where the parameters affecting source and load impedances remain relatively fixed, impedance matching becomes decidedly more difficult in dynamic environments, such as in the context of handheld or portable radio communication devices.
Typical portable communication devices are handheld, meaning that the orientations and positions of their antennas change during usage, such as when a user of a radio cellular telephone changes hands or “crooks” the phone between his or her neck and shoulder. These and other actions change antenna impedance and complicate the task of maintaining a good impedance match between the device's transmitter and the antenna.